Jan. 26, 2024 – The cravings feel inevitable and unavoidable – you stand up, walk to the kitchen, open the fridge or pantry, and ponder. Although you remind yourself to consider a piece of fruit or some protein, your eyes linger on the potato chips and cookies.
If fats and sugars sometimes seem irresistible, you’re not alone. A new study published in Cell Metabolism, based on work by researchers at the Monell Chemical Senses Center in Philadelphia, shows we have two separate but parallel fat and sugar craving pathways that send signals from the gut to the brain, which light up our dopamine reward centers. Even more so, combining these pathways appears to trigger our desire to eat more than usual.
“Over the past few years, we have developed new tools to study the vagus nerve as a pathway of communication between the gut and the brain to control food intake. In this study, we used these tools to understand a simple question that we feel is at the center of the obesity epidemic: Why do we eat foods that we know are bad for us?” said study author Guillaume de Lartigue, PhD, a neuroscientist at Monell who studies the neurobiology of eating. Specifically, the vagus nerve sends internal sensory information through nerve cells in the gut – rather than taste cells in the mouth – which plays a key role in making fats and sugars appealing. Ultimately, the research may indicate what controls “motivated” eating behavior and how a subconscious desire to eat fats and sugars can counteract dieting efforts.
De Lartigue and colleagues used new cutting-edge neuroscience technology to directly manipulate fat or sugar neurons in the vagus nerve system of mice. They found that both types of neurons cause a dopamine release in the brain’s reward center. They also discovered two dedicated vagus nerve pathways – one for fats and one for sugars – that start in the gut and send information about what has been eaten to the brain. This sets the stage for cravings. After that, to understand how fats and sugars affect the brain, the researchers stimulated gut vagal nerves with light. This led the mice to actively seek food to engage these circuits, which demonstrated that fat and sugar are sensed by separate neurons and engage distinct reward circuits, which reinforces cravings.
“The dopamine pathways can also be used to promote healthy behaviors,” Betley said. “We have recently published on the effects of exercise on dopamine levels, suggesting that increasing exercise can change your microbiome and increase the dopamine surge you get from exercising. So these gut-brain communication pathways could be used to also reinforce healthy behaviors – and that our body is wired to allow for this as well.”
Understanding the wiring behind your motivation to eat fats and sugars is the first step toward rewiring it, de Lartigue said. Even when faced with a tempting treat, people could make healthier choices based on personalized intervention plans. “It’s becoming more and more apparent that these mechanisms play a big role in guiding eating behavior and food choice. Given the success of gut-derived peptides (such as Wegovy and Ozempic) for weight loss, it’s essential to understand the gut-brain axis to develop more effective treatments and strategies for weight loss and weight maintenance,” said Alexandra DiFeliceantonio, PhD, a neuroscientist and assistant professor at the Fralin Biomedical Research Institute at Virginia Tech Carilion.